The resistance of the thermally carbonized porous silicon (TCPSi) against HF was utilized to etch a second porous layer underneath the TCPSi sensing layer. Three oxidation methods were studied to obtain electrically isolated TCPSi sensing layers for humidity sensing purposes. The present study showed that electrochemical oxidation is propitious for such applications. The other two methods, pyridine-assisted vapor and liquid oxidations, resulted in cracking at the interface of the TCPSi and oxidized M layers. The TCPSi sensor with an electrically isolated sensing layer was five times more sensitive than a typical TCPSi sensor. (c) 2008 Elsevier B.V. All rights reserved.